Crosslinking of polyolefins can improve the physical properties of articles made therefrom. Moisture-crosslinking is useful for wire-and-cable and crosslinked polyethylene (“PEX”) tubing applications.
For some applications, a liquid, crosslinking-agent “cocktail” is injected or sprayed into the feed section of an extruder, along with pellets of a polyolefin-based product. In some instances, the polyolefin-based product is a base resin, an insulation composition, or a jacket composition. While one of the goals is to adhere the crosslinking-agent cocktail to the pellets, some of the cocktail unfortunately coats part of the extruder.
When the cocktail adheres to part of the extruder, the cocktail may cause slippage of the material along the screw or barrel of the extruder, variation in the volume fed along the screw, flucuations in wall thickness, or unused residue of cocktail in the feed section or on the barrel. To compensate for the unused residue, an additional amount of cocktail is used to permit complete crosslinking. Incomplete crosslinking can adversely effect gel content as well as physical properties such as tensile strength, elongation, hot creep, hot set, and glancing impact. In some instances, the unused residue can harm components of the extruder.
Better incorporation of the liquid, crosslinking-agent cocktail would improve gel content and physical properties of the moisture-cured articles, reduce the amount of cocktail used to compensate for residue losses, and minimize the risk of harm to components of the extruder.